Field of the Invention and Related Art Statement
The present invention relates to an apparatus for detecting an edge position of an article. More particularly, it relates to an apparatus for detecting a substantially linear edge position of an elongated article without bringing the apparatus into contact with the article.
Hitherto, it has been widely practiced to detect the edge position of the elongated article without bringing the apparatus into contact with the article. FIG. 1 is a schematic view showing a conventional apparatus therefor. As clear from FIG. 1, an edge portion 51a of an article 51 is illuminated by a light source 52, and an image of the edge portion 51a is picked-up by a television camera 54 having a onedimensional linear array sensor 53. In the linear array sensor 53 there are provided a plurality of light receiving elements which are linearly arranged in a direction perpendicular to an extending direction of the edge portion 51a of the article 51. The edge position 51a can be obtained by comparing an output signal level of the linear array sensor 53 with an appropriate threshold level.
In the conventional apparatus, since, as shown in FIG. 2, the light receiving elements of the linear array sensor 53 are arranged substantially perpendicular to the extending direction of the edge portion 51a of the article 51, a single point on the edge portion at which the linear image sensor 53 and the edge portion 51a intersect with each other is detected and the thus detected point is regarded as the edge position of the article. Thus, when the length of the article is measured on the basis of the thus obtained position of the edge portion, if a defect 55 is formed in the edge portion of the article and the image sensor 53 intersects with the edge portion at the defect as shown in FIG. 2, the length of the article could not be measured correctly. Thus, the conventional apparatus has a drawback that the detecting result is apt to be largely affected by a defect, dust or an obstacle formed in or adhered to the edge portion of the article to be measured.
A tread rubber for use in manufacturing tires is liable to have such a defect or dust in the edge portion thereof due to the transportation or handling after cutting the tread rubber. Further the edge portion of the tread rubber is usually cut obliquely in order to join tread rubbers to each other by putting over the obliquely cut edge portions successively. Therefore, when the article to be measured is the tread rubber, the measured length thereof might be varied depending upon the point at which the linear array sensor intersects with the edge portion of the tread rubber. In order to reduce the affect caused by the defect or dust formed in or adhered on the edge portion of the tread rubber, it would be suggested to detect the edge position at two or more points and to derive a mean value of the detected results. However, if there is a defect or dust at one of these points, it is not possible to measure the length of the tread rubber accurately and the reliability of the measurement becomes low because any error caused by the defect or the dust in the edge portion of the article will be still in the measurement results.